U.S. patent number 6,706,791 [Application Number 09/825,039] was granted by the patent office on 2004-03-16 for cable semiconductive shield compositions.
This patent grant is currently assigned to Nippon Unicar Company Limited. Invention is credited to Koji Ishihara, Ariyoshi Ohki, Kiroku Tsukada.
United States Patent |
6,706,791 |
Tsukada , et al. |
March 16, 2004 |
Cable semiconductive shield compositions
Abstract
A composition comprising: (a) one or more copolymers selected
from the group consisting of (I) a copolymer of ethylene and vinyl
acetate containing about 10 to about 50 percent by weight vinyl
acetate and having a melt mass flow rate of about 1 to about 100
grams per 10 minutes; (II) a copolymer of ethylene and ethyl
acrylate containing about 10 to about 50 percent by weight ethyl
acrylate and having a melt mass flow rate of about 1 to about 100
grams per 10 minutes; and (III) a copolymer of ethylene and butyl
acrylate containing about 10 to about 50 percent by weight butyl
acrylate and having a melt mass flow rate of about 1 to about 100
grams per 10 minutes, and based upon 100 parts by weight of
component (a): (b) about 55 to about 200 parts by weight of a
linear copolymer of ethylene and an alpha-olefin having 3 to 12
carbon atoms, the copolymer having a melt mass flow rate of about
0.1 to about 30 grams per 10 minutes and a density of 0.870 to
0.944 gram per cubic centimeter; (c) about 5 to about 50 parts by
weight of polypropylene having a melt mass flow rate of about 0.5
to about 30 grams per 10 minutes and a density of 0.900 to 0.920
gram per cubic centimeter; (d) about 2 to about 50 parts by weight
of an organopolysiloxane having the following formula:
R.sup.1.sub.x R.sup.2.sub.y SiO.sub.(4-a-b)/2 wherein R.sup.1 is an
aliphatic unsaturated hydrocarbon group; R.sup.2 is an
unsubstituted or substituted monovalent hydrocarbon group excluding
aliphatic unsaturated hydrocarbon groups; x is equal to or greater
than 0 but less than 1; y is greater than 0.5 but less than 3; x+y
is greater than 1 but less than 3; a is greater than 0 but equal to
or less than 1; and b is equal to or greater than 0.5 but equal to
or less than 3; (e) about 10 to about 350 parts by weight of carbon
black; and (f) optionally, up to about 2 parts by weight of an
organic peroxide.
Inventors: |
Tsukada; Kiroku (Yokohama,
JP), Ohki; Ariyoshi (Yokohama, JP),
Ishihara; Koji (Tokyo, JP) |
Assignee: |
Nippon Unicar Company Limited
(Tokyo, JP)
|
Family
ID: |
26458425 |
Appl.
No.: |
09/825,039 |
Filed: |
April 3, 2001 |
Current U.S.
Class: |
524/261;
524/495 |
Current CPC
Class: |
C08K
5/1345 (20130101); C08K 5/14 (20130101); C08L
23/08 (20130101); C08K 5/1345 (20130101); C08L
23/08 (20130101); C08K 5/14 (20130101); C08L
23/08 (20130101); C08L 23/08 (20130101); C08L
23/0815 (20130101); C08L 23/0853 (20130101); C08L
23/0869 (20130101); C08L 23/10 (20130101); C08L
2203/202 (20130101); C08L 2205/02 (20130101); C08L
2666/04 (20130101) |
Current International
Class: |
C08L
23/08 (20060101); C08L 23/00 (20060101); C08K
5/00 (20060101); C08K 5/14 (20060101); C08K
5/134 (20060101); C08L 23/10 (20060101); C08K
003/04 () |
Field of
Search: |
;524/261,495 |
References Cited
[Referenced By]
U.S. Patent Documents
|
|
|
6525119 |
February 2003 |
Tsukada et al. |
|
Primary Examiner: Cain; Edward J.
Claims
What is claimed is:
1. A composition comprising: (a) one or more copolymers selected
from the group consisting of (I) a copolymer of ethylene and vinyl
acetate containing about 10 to about 50 percent by weight vinyl
acetate and having a melt mass flow rate of about 1 to about 100
grams per 10 minutes; (II) a copolymer of ethylene and ethyl
acrylate containing about 10 to about 50 percent by weight ethyl
acrylate and having a melt mass flow rate of about 1 to about 100
grams per 10 minutes; and (III) a copolymer of ethylene and butyl
acrylate containing about 10 to about 50 percent by weight butyl
acrylate and having a melt mass flow rate of about 1 to about 100
grams per 10 minutes, and based upon 100 parts by weight of
component (a): (b) about 55 to about 200 parts by weight of a
linear copolymer of ethylene and an alpha-olefin having 3 to 12
carbon atoms, the copolymer having a melt mass flow rate of about
0.1 to about 30 grams per 10 minutes and a density of 0.870 to
0.944 gram per cubic centimeter; (c) about 5 to about 50 parts by
weight of polypropylene having a melt mass flow rate of about 0.5
to about 30 grams per 10 minutes and a density of 0.900 to 0.920
gram per cubic centimeter; (d) about 2 to about 50 parts by weight
of an organopolysiloxane having the following formula:
R.sup.1.sub.x R.sup.2.sub.y SiO.sub.(4-a-b)/2 wherein R.sup.1 is an
aliphatic unsaturated hydrocarbon group; R.sup.2 is an
unsubstituted or substituted monovalent hydrocarbon group excluding
aliphatic unsaturated hydrocarbon groups; x is equal to or greater
than 0 but less than 1; y is greater than 0.5 but less than 3; x+y
is greater than 1 but less than 3; a is greater than 0 but equal to
or less than 1; and b is equal to or greater than 0.5 but equal to
or less than 3; (e) about 10 to about 350 parts by weight of carbon
black; and (f) optionally, up to about 2 parts by weight of an
organic peroxide.
2. The composition defined in claim 1 wherein the ester in
component (a) is present in an amount of about 15 to about 40
percent by weight.
3. The composition defined in claim 1 wherein the components are
present in the following amounts: (b) about 75 to about 100 parts
by weight; (c) about 15 to about 30 parts by weight; (d) about 2 to
about 10 parts by weight; (e) about 40 to about 300 parts by
weight; and (f) about 0.15 to about 0.8 part by weight.
4. The composition defined in claim 1 wherein component (b) is
LLDPE or VLDPE.
5. The composition defined in claim 1 wherein component (d) is a
silicone gum or a silicone oil.
6. The composition defined in claim 1 wherein component (e) is
Ketjen black.
7. The composition defined in claim 1 wherein the organic peroxide
has a 10 minute half life at 100 to 220 degrees C.
8. A cable comprising an electrical conductor or a core of
electrical conductors surrounded by a moisture cured insulation
layer, which is surrounded by, and contiguous with, a
semiconductive layer, said semiconductive layer comprising: (a) one
or more copolymers selected from the group consisting of (I) a
copolymer of ethylene and vinyl acetate containing about 10 to
about 50 percent by weight vinyl acetate and having a melt mass
flow rate of about 1 to about 100 grams per 10 minutes; (II) a
copolymer of ethylene and ethyl acrylate containing about 10 to
about 50 percent by weight ethyl acrylate and having a melt mass
flow rate of about 1 to about 100 grams per 10 minutes; and (III) a
copolymer of ethylene and butyl acrylate containing about 10 to
about 50 percent by weight butyl acrylate and having a melt mass
flow rate of about 1 to about 100 grams per 10 minutes, and based
upon 100 parts by weight of component (a): (b) about 55 to about
200 parts by weight of a linear copolymer of ethylene and an
alpha-olefin having 3 to 12 carbon atoms, the copolymer having a
melt mass flow rate of about 0.1 to about 30 grams per 10 minutes
and a density of 0.870 to 0.944 gram per cubic centimeter; (c)
about 5 to about 50 parts by weight of polypropylene having a melt
mass flow rate of about 0.5 to about 30 grams per 10 minutes and a
density of 0.900 to 0.920 gram per cubic centimeter; (d) about 2 to
about 50 parts by weight of an organopolysiloxane having the
following formula: R.sup.1.sub.x R.sup.2.sub.y SiO.sub.(4-a-b)/ 2
wherein R.sup.1 is an aliphatic unsaturated hydrocarbon group;
R.sup.2 is an unsubstituted or substituted monovalent hydrocarbon
group excluding aliphatic unsaturated hydrocarbon groups; x is
equal to or greater than 0 but less than 1; y is greater than 0.5
but less than 3; x+y is greater than 1 but less than 3; a is
greater than 0 but equal to or less than 1; and b is equal to or
greater than 0.5 but equal to or less than 3; and (e) about 10 to
about 350 parts by weight of carbon black.
9. The cable defined in claim 8 wherein component (d) is grafted to
one or more of components (a), (b), and (c).
Description
TECHNICAL FIELD
This invention relates to a power cable having a semiconductive
shield and moisture cured insulation.
BACKGROUND INFORMATION
A typical electric power cable generally comprises one or more
conductors in a cable core that is surrounded by several layers of
polymeric materials including a first (internal) semiconductive
shield layer (conductor or strand shield), an insulating layer, a
second semiconductive shield layer (insulation shield or external
semiconductive layer), a metallic tape or wire shield, and a
protective jacket. The external semiconductive shield can be either
bonded to the insulation or strippable, with most applications
using strippable shields. Additional layers within this
construction such as moisture impervious materials are often
incorporated.
Polymeric semiconductive shields have been utilized in multilayered
power cable construction for many decades. Generally, they are used
to fabricate solid dielectric power cables rated for voltages
greater than 1 kilo Volt (kV). These shields are used to provide
layers of intermediate conductivity between the high potential
conductor and the primary insulation, and between the primary
insulation and the ground or neutral potential. The volume
resistivity of these semiconductive materials is typically in the
range of 10.sup.-1 to 10.sup.8 ohm-centimeters when measured on a
completed power cable construction using the methods described in
ICEA S-66-524, section 6.12, or IEC 60502-2 (1997), Annex C.
Typical strippable internal or external shield compositions contain
a polyolefin, such as ethylene/vinyl acetate copolymer with a high
vinyl acetate content, conductive carbon black, an organic peroxide
crosslinking agent, and other conventional additives such as a
nitrile rubber, which functions as a strip force reduction aid,
processing aids, and antioxidants. These compositions are usually
prepared in granular or pellet form. Polyolefin formulations such
as these are disclosed in U.S. Pat. No. 4,286,023 and European
Patent Application 420 271. The shield composition is, typically,
introduced into an extruder where it is co-extruded around an
electrical conductor at a temperature lower than the decomposition
temperature of the organic peroxide to form a cable. The cable is
then exposed to higher temperatures at which the organic peroxide
decomposes to provide free radicals, which crosslink the polymer.
The electrical conductor can be, for example, made of annealed
copper, semihard drawn copper, hard drawn copper, or aluminum.
Polyethylenes, which are typically used as the polymeric component
in the insulation layer, can be made moisture curable by making the
resin hydrolyzable, which is accomplished by adding hydrolyzable
groups such as --Si(OR).sub.3 wherein R is a hydrocarbyl radical to
the resin structure through conventional copolymerization or
grafting techniques. Grafting can be effected at 210 to 250 degrees
C. Suitable crosslinking agents are organic peroxides such as
dicumyl peroxide; 2,5-dimethyl-2,5-di(t-butylperoxy)hexane; t-butyl
cumyl peroxide; and 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3.
Dicumyl peroxide is preferred. The amount of organic peroxide used
in the grafting process can be in the range of 0.01 to 4 parts by
weight per 100 parts by weight of the base resin.
Suitable alkoxysilane compounds, which can be used to provide the
hydrolyzable group can be represented by the following formula:
RR'SiY.sub.2 wherein R is an aliphatic unsaturated hydrocarbon
group or a hydrocarbonoxy group, R' is a hydrogen atom or a
saturated monovalent hydrocarbon group, and Y is an alkoxy group.
Examples of R are vinyl, allyl, butenyl, cyclohexenyl, and
cyclopentadienyl. The vinyl group is preferred. Examples of Y are
ethoxy, methoxy, and butoxy.
Examples of ethylenically unsaturated alkoxysilanes are vinyl
triethoxysilane, vinyl trimethoxysilane, and
gamma-methacryloxypropyltrimethoxy-silane. The amount of
alkoxysilane compound that can be used is preferably about 0.5 to
about 20 parts by weight per 100 parts by weight of base resin.
Hydrolyzable groups can be added, for example, by copolymerizing
ethylene with an ethylenically unsaturated compound having one or
more --Si(OR).sub.3 groups or grafting these silane compounds to
the resin in the presence of the aforementioned organic peroxides.
The hydrolyzable resins are then crosslinked by moisture, e.g.,
steam or hot water, in the presence of a silanol condensation
catalvst such as dibutyltin dilaurate, dioctyltin maleate,
dibutyltin diacetate, stannous acetate, lead naphthenate, and zinc
caprylate. Dibutyltin dilaurate is preferred. The amount of silanol
condensation catalyst can be in the range of about 0.001 to about
20 parts by weight per 100 parts by weight of base resin, and is
preferably about 0.005 to about 5 parts by weight.
Examples of hydrolyzable copolymers and hydrolyzable grafted
copolymers are ethylene/vinyltrimethoxy silane copolymer,
ethylene/gamma-methacryloxypropyltrimethoxy silane copolymer,
vinyltrimethoxy silane grafted ethylene/ethyl acrylate copolymer,
vinyltrimethoxy silane grafted linear low density ethylene/1-butene
copolymer, and vinyltrimethoxy silane grafted low density
polyethylene.
In applications where moisture cured insulation is used, it is
desirable to provide a moisture cured strippable semiconductive
shield to protect the insulation. The shield composition would then
be prepared in the same manner as the moisture cured insulation as
outlined above. Unfortunately, shield compositions, which could be
moisture cured, were found to have a tendency to scorch, i.e., to
prematurely crosslink during extrusion. In addition to solving the
scorch problem, the shield had to be easily strippable by hand or
with the aid of an appropriate tool.
Further, the use of a peroxide crosslinkable insulation shield over
a moisture curable insulation is not considered viable because of
the incompatibility of the processing requirements for each.
Typically, the peroxide system utilizes higher operating
temperatures during the cure cycle, and these high temperatures
interfere with the dimensional stability of the "uncured" moisture
curable insulation. The upshot is that the peroxide system requires
a pressurized curing tube, which is an integral part of the
extrusion process, while the moisture curable insulation is cured
in a post extrusion stage. It was also found that while
crosslinking via a peroxide did improve scorch, it did not enhance
strippability.
It is apparent, then, that both the peroxide system and the
moisture cure system for the insulation shield each have their
drawbacks. Further, it is found especially desirable that the
insulation shield have the following characteristics: (1) a volume
specific resistance of 100 ohm-centimeters or less to prevent
corona degradation caused by partial delamination and gap
formation; (2) an elongation of 100 percent or more to maintain
elasticity, and prevent partial delamination and gap formation when
the power cable is bent or is exposed in the heat cycle; (3) a
smooth interface between the moisture cured insulation layer and
the insulation shield with an absence of micro-protrusions; (4)
capable of being extruded high temperatures similar to the
temperatures used for the moisture cured insulation layer, i.e.,
210 to 250 degrees C.; (5) a tensile strength of 10 Mpa or more so
that the insulation shield will not be cut during stripping; (6) a
cold temperature resistance; (7) a peel strength of 4 kilograms per
0.5 inch or less to provide for easy stripping from the moisture
cured insulation layer; and (8) a heat deformation at 120 degrees
C. of 40 percent or less.
DISCLOSURE OF THE INVENTION
An object of this invention, therefore, is to provide a composition
useful for an insulation shield for a moisture cured insulation
layer, which has the above characteristics and avoids the drawbacks
of peroxide and moisture cured shields. Other objects and
advantages will become apparent hereinafter.
According to the invention, such a composition has been discovered.
The composition comprises: (a) one or more copolymers selected from
the group consisting of (I) a copolymer of ethylene and vinyl
acetate containing about 10 to about 50 percent by weight vinyl
acetate and having a melt mass flow rate of about 1 to about 100
grams per 10 minutes; (II) a copolymer of ethylene and ethyl
acrylate containing about 10 to about 50 percent by weight ethyl
acrylate and having a melt mass flow rate of about 1 to about 100
grams per 10 minutes; and (III) a copolymer of ethylene and butyl
acrylate containing about 10 to about 50 percent by weight butyl
acrylate and having a melt mass flow rate of about 1 to about 100
grams per 10 minutes, and based upon 100 parts by weight of
component (a): (b) about 55 to about 200 parts by weight of a
linear copolymer of ethylene and an alpha-olefin having 3 to 12
carbon atoms, the copolymer having a melt mass flow rate of about
0.1 to about 30 grams per 10 minutes and a density of 0.870 to
0.944 gram per cubic centimeter; (c) about 5 to about 50 parts by
weight of polypropylene having a melt mass flow rate of about 0.5
to about 30 grams per 10 minutes and a density of 0.900 to 0.920
gram per cubic centimeter; (d) about 2 to about 50 parts by weight
of an organopolysiloxane having the following formula:
R.sup.1.sub.x R.sup.2.sub.y SiO.sub.(4-a-b)/ 2 wherein R.sup.1 is
an aliphatic unsaturated hydrocarbon group; R.sup.2 is an
unsubstituted or substituted monovalent hydrocarbon group excluding
aliphatic unsaturated hydrocarbon groups; x is equal to or greater
than 0 but less than 1; y is greater than 0.5 but less than 3; x+y
is greater than 1 but less than 3; a is greater than 0 but equal to
or less than 1; and b is equal to or greater than 0.5 but equal to
or less than 3; (e) about 10 to about 350 parts by weight of carbon
black; and (f) optionally, up to about 2 parts by weight of an
organic peroxide.
DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
The resins most commonly used in semiconductive shields are
elastomers of varying degrees of crystallinity from amorphous
through low and medium crystallinity. These elastomers are
typically ethylene/unsaturated ester copolymers, which are usually
made by conventional high pressure free radical processes generally
run at pressures above 15,000 psi (pounds per square inch). The
ethylene/unsaturated ester copolymers used in this invention are
set forth in component (a), above, i.e., one or more copolymers
selected from the group consisting of (I) a copolymer of ethylene
and vinyl acetate containing about 10 to about 50 percent,
preferably about 15 to about 40 percent, by weight vinyl acetate
and having a melt mass flow rate of about 1 to about 100 grams per
10 minutes; (II) a copolymer of ethylene and ethyl acrylate
containing about 10 to about 50 percent, preferably about 15 to
about 40 percent, by weight ethyl acrylate and having a melt mass
flow rate of about 1 to about 100 grams per 10 minutes; and (III) a
copolymer of ethylene and butyl acrylate containing about 10 to
about 50 percent, preferably about 15 to about 40 percent, by
weight butyl acrylate and having a melt mass flow rate of about 1
to about 100 grams per 10 minutes. The percent by weight is based
on the total weight of the copolymer. Melt mass flow rate is
determined under JIS (Japanese Industrial Standard) K-6760. It is
measured at 190.degree. C. and 21.6 kilograms in grams per 10
minutes.
Component (b) is about 55 to about 200, preferably about 75 to
about 150, parts by weight of a linear copolymer of ethylene and an
alpha-olefin having 3 to 12 carbon atoms, the copolymer having a
melt mass flow rate of about 0.1 to about 30 grams per 10 minutes
and a density of 0.870 to 0.944 gram per cubic centimeter. The
ethylene polymers useful in subject invention are preferably
produced in the gas phase. They can also be produced in the liquid
phase in solutions or slurries by conventional techniques. They are
usually produced by low pressure processes, which are typically run
at pressures below 1000 psi. Typical catalyst systems, which can be
used to prepare these polymers are magnesium/titanium based
catalyst systems, which can be exemplified by the catalyst system
described in U.S. Pat. No. 4,302,565; vanadium based catalyst
systems such as those described in U.S. Pat. Nos. 4,508,842 and
5,332,793; 5,342,907; and 5,410,003; a chromium based catalyst
system such as that described in U.S. Pat. No. 4,101,445; a
metallocene catalyst system such as that described in U.S. Pat.
Nos. 4,937,299 and 5,317,036; or other transition metal catalyst
systems. Many of these catalyst systems are often referred to as
Ziegler-Natta catalyst systems. Catalyst systems, which use
chromium or molybdenum oxides on silica-alumina supports, are also
useful. Typical processes for preparing the polymers are also
described in the aforementioned patents. Blends of these copolymers
can be used if desired. Typical in situ polymer blends and
processes and catalyst systems for providing same are described in
U.S. Pat. Nos. 5,371,145 and 5,405,901. The linear copolymers can
be, among others, LLDPE or VLDPE.
The linear low density polyethylene (LLDPE) can have a density in
the range of 0.916 to 0.925 gram per cubic centimeter. It can be a
copolymer of ethylene and one or more alpha-olefins having 3 to 12
carbon atoms, and preferably 3 to 8 carbon atoms. The preferred
alpha-olefins can be exemplified by propylene, 1-butene, 1-hexene,
4-methyl-1-pentene, and 1-octene, and the catalysts and processes
can be the same as those mentioned above subject to variations
necessary to obtain the desired densities and melt indices.
The very low density polyethylene (VLDPE) can also be a copolymer
of ethylene and one or more alpha-olefins having 3 to 12 carbon
atoms and preferably 3 to 8 carbon atoms. Preferred alpha-olefins
are mentioned above. The density of the VLDPE can be in the range
of 0.870 to 0.915 gram per cubic centimeter. It can be produced
using the catalysts and processes mentioned above. The portion of
the VLDPE attributed to the comonomer(s), other than ethylene, can
be in the range of about 1 to about 49 percent by weight based on
the weight of the copolymer and is preferably in the range of about
15 to about 40 percent by weight. A third comonomer can be
included, e.g., another alpha-olefin or a diene such as ethylidene
norbornene, butadiene, 1,4-hexadiene, or a dicyclopentadiene. The
third comonomer can be present in an amount of about 1 to 15
percent by weight based on the weight of the copolymer and is
preferably present in an amount of about 1 to about 10 percent by
weight. It is preferred that the copolymer contain two or three
comonomers inclusive of ethylene.
Component (c) is about 5 to about 50, preferably about 15 to about
30, parts by weight of polypropylene having a melt mass flow rate
of about 0.5 to about 30 grams per 10 minutes and a density of
0.900 to 0.920 gram per cubic centimeter. The polypropylene can be
a homopolymer of propylene or a copolymer of propylene and an
alpha-olefin having 2 or 4 to 12 carbon atoms wherein the portion
of the copolymer based on propylene is at least about 60 percent by
weight based on the weight of the copolymer. Examples of the
alpha-olefins are mentioned above. The polypropylene can be
prepared by conventional processes such as the process described in
U.S. Pat. No. 4,414,132.
Component (d) is about 2 to about 50, preferably about 2 to about
10, parts by weight of an organopolysiloxane having the following
formula: R.sup.1.sub.x R.sup.2.sub.y SiO.sub.(4-a-b)/ 2 wherein
R.sup.1 is an aliphatic unsaturated hydrocarbon group; R.sup.2 is
an unsubstituted or substituted monovalent hydrocarbon group
excluding aliphatic unsaturated hydrocarbon groups; x is equal to
or greater than 0 but less than 1; y is greater than 0.5 but less
than 3; x+y is greater than 1 but less than 3; a is greater than 0
but equal to or less than 1; and b is equal to or greater than 0.5
but equal to or less than 3.
In the organopolysiloxane expressed by the aforementioned formula,
R.sup.1 can be, for example, a vinyl, allyl, acryl, or methacryl
group, and R.sup.2 can be an alkyl group such as methyl, ethyl, or
propyl; an aryl group such as phenyl or tolyl; a cycloalkyl group
such as cyclohexyl or cyclobutyl. The R.sup.2 groups can be
substituted with various substituents such as halogen atoms, or
cyano or mercapto.
Organopolysiloxanes, which can be used in the present invention,
can be exemplified by linear, branched, cyclic, network, or stereo
network structures provided that the molecular structure is within
the formula, but the linear structure is preferable. The degree of
polymerization of the organopolysiloxane is not particularly
limited, but it preferably has a degree of polymerization which
does not inhibit kneading with the ethylene copolymer.
One organopolysiloxane, which can be used is silicone gum. Another
linear organopolysiloxane can be represented by the following
formula: R.sub.3 --Si--O--(R.sub.2 --Si--O)n--R.sub.3 wherein R is
a substituted or unsubstituted monovalent hydrocarbon and n is at
least 10. This compound is generally referred to as a silicone oil.
R can be an alkyl or aryl group and hydrogen. Examples of the alkyl
group are methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl,
and t-butyl. An example of the aryl group is phenyl. The Rs can be
the same or different except that the Rs cannot all be hydrogen,
and part of the R can be, for example, vinyl or hydroxyl; n can be
10 to 10,000 and is preferably 100 to 1000. It is desirable that
the viscosity of the organopolysiloxane in liquid form is a least
about 10 centistokes, and is preferably about 1000 to about
1,000,000 centistokes, at 23 degrees C.
Component (e): In order to provide a semiconductive shield it is
necessary to incorporate conductive particles into the composition.
These conductive particles are generally provided by particulate
carbon black, which is referred to above. Useful carbon blacks can
have a surface area of about 50 to about 1000 square meters per
gram. The surface area is determined under ASTM D 4820-93a
(Multipoint B.E.T. Nitrogen Adsorption). The carbon black can be
used in the semiconductive shield composition in an amount of about
10 to about 350 parts by weight, and preferably about 40 to about
300 parts by weight. An objective is to keep the volume specific
resistance at less than about 100 ohm-centimeters. Both standard
conductivity and high conductivity carbon blacks can be used with
standard conductivity blacks being preferred. Examples of
conductive carbon blacks are the grades described by ASTM N550,
N472, N351, N110, acetylene black, furnace black, and Ketjen black.
The Ketjen black is particularly desirable as one third to one half
the amount of Ketjen black provides the same level of conductivity
as the full amount of a conventional carbon black.
Optionally, the following copolymer can be included in
semiconductive shield compositions: a copolymer of acrylonitrile
and butadiene wherein the acrylonitrile is present in an amount of
about 30 to about 60 percent by weight based on the weight of the
copolymer, and is preferably present in an amount of about 40 to
about 50 percent by weight. This copolymer is also known as a
nitrile rubber or an acrylonitrile/butadiene copolymer rubber. The
density can be, for example, 0.98 gram per cubic centimeter and the
Mooney Viscosity can be (ML 1+4) 50. A silicone rubber can be
substituted for this copolymer (f) Organic peroxide component. As
noted, this component is optional, but it is preferred that it be
in the insulation shield composition. The organic peroxide has an
(O--O) bond in the molecule, and it is preferable that it has a 10
minute half life at 100 to 220 degrees C. It assists the filling
and dispersing properties of the carbon black by grafting
components (a) through (d), and not initiating a crosslinking
reaction with respect to these components. Examples of suitable
organic peroxides follow (the figure in parenthesis is the
decomposition temperature of the organic peroxide in degrees C.):
succinic acid peroxide (110), benzoyl peroxide (110),
t-butylperoxy-2-ethylhexanoate (113), p-chlorobenzoyl peroxide
(115), t-butylperoxyisobutyrate (115),
t-butylperoxyisopropylcarbonate (135), t-butylperoxylaurate (140),
2,5-dimethyl-2,5-di(benzoylperoxy)hexane (140),
t-butylperoxyacetate (140), di-tbutyldiperoxyphthalate (140),
t-butylperoxybenzoate (145), dicumyl peroxide (150),
2,5-dimethyl-2,5-di(t-butylperoxy)hexane (155), tbutylcumyl
peroxide (155), t-butylhydroperoxide (158), di-t-butyl peroxide
(160), 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3 (170),
di-isopropylbenzenehydroperoxide (170), p-menthanehydroperoxide
(180), 2,5-dimethylhexane-2,5-dihydroperoxide (213), and
cumenehydroperoxide (149). Among these, cumyl peroxide,
2,5-dimethyl-2,5-(tbutylperoxy)hexane, and cumenehydroperoxide are
preferred.
The blending amount of the organic peroxide is up to about 2 parts
by weight, and is preferably in the range of about 0.15 to about
0.8 part by weight, and more preferably in the range of about 0.3
to about 0.6 part by weight. Its function is to initiate a graft
reaction between components (a) through (d), particularly
components (a) and (d).
The insulation shield composition can be prepared in the following
ways: (i) Component (d) can be grafted to component (a) by kneading
while heating at about 220 degrees C. Then all of the components
can be fed into an extruder. (ii) Component (d) can be grafted to
component (a) by heating at about 160 degrees C. in the presence of
an organic peroxide. Then all of the components can be fed into an
extruder. (iii) The polymers can be grafted to one another by
kneading components (a), (b), (c), (d) and (f) together while
heating at about 165 degrees C.
Conventional additives, which can be introduced into the
composition, are exemplified by antioxidants, coupling agents,
ultraviolet absorbers or stabilizers, antistatic agents, pigments,
dyes, nucleating agents, reinforcing fillers or polymer additives,
slip agents, plasticizers, processing aids, lubricants, viscosity
control agents, tackifiers, anti-blocking agents, surfactants,
extender oils, metal deactivators, voltage stabilizers, flame
retardant fillers and additives, crosslinking agents, boosters, and
catalysts, and smoke suppressants. Additives and fillers can be
added in amounts ranging from less than about 0.1 to more than
about 50 percent by weight based on the weight of the
composition.
Examples of antioxidants are: hindered phenols such as tetrakis
[methylene(3,5-di-tert-butyl-4-hydroxyhydrocinnamate)] methane, bis
[(beta-(3,5-ditert-butyl-4-hydroxybenzyl)methylcarboxyethyl)]
sulphide, 4,4'-thiobis(2-methyl-6-tert-butylphenol),
4,4'-thiobis(2-tert-butyl-5-methylphenol),
2,2'-thiobis(4-methyl-6-tert-butylphenol), and thiodiethylene
bis(3,5-di-tert-butyl-4-hydroxy)hydrocinnamate; phosphites and
phosphonites such as tris(2,4-di-tert-butylphenyl)phosphite and
di-tert-butylphenyl-phosphonite; thio compounds such as
dilaurylthiodipropionate, dimyristylthiodipropionate, and
distearylthiodipropionate; various siloxanes; and various amines
such as polymerized 2,2,4-trimethyl-1,2-dihydroquinoline,
4,4'-bis(alpha,alpha-demthylbenzyl)diphenylamine, and alkylated
diphenylamines. Antioxidants can be used in amounts of about 0.001
to about 5 percent by weight based on the weight of the
composition.
Compounding can be effected in a conventional melt/mixer or in a
conventional extruder, and these terms are used in this
specification interchangeably. Generally, the conductive shield
composition is prepared in a melt/mixer and then pelletized using a
pelletizer attachment or an extruder adapted for pelletizing. Both
the melt/mixer, as the name implies, and the extruder, in effect,
have melting and mixing zones although the various sections of each
are known to those skilled in the art by different names. The
semiconductive shield composition of the invention can be prepared
in various types of melt/mixers and extruders such as a
Brabender.TM. mixer, Banbury.TM. mixer, a roll mill, a Buss.TM.
co-kneader, a biaxial screw kneading extruder, and single or twin
screw extruders. A description of a conventional extruder can be
found in U.S. Pat. No. 4,857,600. In addition to melt/mixing, the
extruder can coat a wire or a core of wires. An example of
co-extrusion and an extruder therefor can be found in U.S. Pat. No.
5,575,965. A typical extruder has a hopper at its upstream end and
a die at its downstream end. The hopper feeds into a barrel, which
contains a screw. At the downstream end, between the end of the
screw and the die, is a screen pack and a breaker plate. The screw
portion of the extruder is considered to be divided up into three
sections, the feed section, the compression section, and the
metering section, and two zones, the back heat zone and the front
heat zone, the sections and zones running from upstream to
downstream. In the alternative, there can be multiple heating zones
(more than two) along the axis running from upstream to downstream.
If it has more than one barrel, the barrels are connected in
series. The length to diameter ratio of each barrel is in the range
of about 15:1 to about 30:1. In wire coating, where the material is
crosslinked after extrusion, the die of the crosshead feeds
directly into a heating zone, and this zone can be maintained at a
temperature in the range of about 130.degree. C. to about
260.degree. C., and preferably in the range of about 170.degree. C.
to about 220.degree. C. Double layer simultaneous extruding
machines and triple layer simultaneous extruding machines are
advantageously used to prepare the power cable with the various
layers described above.
The advantages of the invention are excellent semiconductivity,
strippability, tensile strength, processability, surface
smoothness, cold temperature resistance, and heat endurance The
term "surrounded" as it applies to a substrate being surrounded by
an insulating composition, jacketing material, or other cable layer
is considered to include extruding around the substrate; coating
the substrate; or wrapping around the substrate as is well known by
those skilled in the art. The substrate can include, for example, a
core including a conductor or a bundle of conductors, or various
underlying cable layers as noted above.
All molecular weights mentioned in this specification are weight
average molecular weights unless otherwise designated.
The patents mentioned in this specification are incorporated by
reference herein.
The invention is illustrated by the following examples
EXAMPLES
The experimental methods in the examples are as follows.
(1) Interface Smoothness:
The interface between the moisture crosslinked polyethylene
insulation layer and the external semiconductive layer (insulation
shield) is evaluated visually.
(2) Heat Deformation Rate of the External Semiconductive Layer:
The heat endurance of the external semiconductive layer at 120
degrees C. is determined by following test in accordance with JIS
C3005: Heat deformation test method.
(i) Preparation of Test Piece
The strippable semiconductive resin composition for the external
semiconductive layer is kneaded by heating at 220 degrees C., a
plate shaped piece 2 millimeters thick, 15 millimeters wide, and 30
millimeters long is molded by a hot press molder, and it is used as
the test piece.
(ii) Determination Method
The test piece is placed on a semicircular part of a semicircular
bar of 5 millimeters in diameter; a parallel plate is stacked on
the test piece; it is heated in an oven at 120 degrees C. for 30
minutes, then 2 kilograms of pressure is loaded onto the parallel
plate, allowed to stand for 30 minutes, and the thickness of the
test piece is measured. A thickness decrease rate is then
determined.
(3) Peeling Test of the External Semi-conductive Layer: It is
Performed by Following Method.
(i) Preparation of Test Piece
The moisture crosslinking polyethylene resin composition is kneaded
by heating at 220 degrees C. and a sheet 1.5 millimeters thick, 150
millimeters long and 180 millimeters wide is prepared with a hot
press molder. On the other hand, the strippable semiconductive
resin composition for the external semiconductive layer is kneaded
by heating at 200 degrees C., and a sheet 2 millimeters thick, 150
millimeters long and 180 millimeters wide is prepared with a hot
press molder. Both sheets are unified at a temperature of 180
degrees C. and a pressure of 15 MPa to make a 3 millimeter thick
sheet, and it is moisture crosslinked in steam at 80 degrees C. for
24 hours. A test piece 12.5 millimeters in width and 120
millimeters long is stamped out from the double layer sheet.
(ii) Test Method
A peeling test with a pulling rate of 500 millimeters per minute at
23 degrees C. is performed by using a tensile machine, and a force
to peel the external semiconductive layer from the moisture
crosslinked polyethylene layer at an angle of 180 degrees is
determined as a peel strength in kilograms per 0.5 inch.
(4) Tensile Strength of the External Semiconductive Layer
The strippable semiconductive resin composition for the external
semiconductive layer is kneaded by heating at 200 degrees C. and a
sheet 2 millimeters thick, 150 millimeters long and 180 millimeters
wide is prepared with a hot press molder, it is tested as a test
piece, and a tensile strength is determined under JIS K-6760.
(5) Elongation of the External Semi-conductive Layer
Elongation is determined under JIS K-6760 by using a test piece
prepared in the same manner as for tensile strength.
(6) Gel Fraction of the Moisture Crosslinked Polyethylene
Insulation Layer
A sample is taken from the moisture crosslinked polyethylene
insulation layer; it is immersed in xylene at 110 degrees C. for 24
hours, and the extraction residue is determined as the gel
fraction.
(7) Extrusion Processability
Melt mass flow rate of the strippable semiconductive resin
composition for external semi-conductive layer is evaluated by
determining the melt mass flow rate under conditions of 190 degrees
C. and a 21.6 kilogram load by using a melt indexer (JIS
K-6760).
(8) Volume Specific Resistance
The volume specific resistance of the strippable semiconductive
resin composition for the external semiconductive layer is
determined under JIS K-6723.
Example 1
(A) Preparation of the resin composition for the internal
semiconductive layer: 0.5 part by weight of
tetrakis[methylene-3-(3,5-t-butyl-4-hydroxyphenyl)propionate]methane
and 80 parts by weight of acetylene black are blended with 100
parts by weight of a high pressure process ethylene/vinyl acetate
copolymer containing 28 percent by weight vinyl acetate, and having
a melt mass flow rate of 20 grams per 10 minutes and a melting
point of 91 degrees C. The three components are kneaded at 130
degrees C. for 10 minutes, and cylindrically pelletized to pellets,
each 3 millimeters in diameter and 3 millimeters in height. Then,
0.5 part by weight of 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne, an
organic peroxide, is added to the pellets; the organic peroxide is
evenly impregnated into in the pellets by slow mixing at 70 degrees
C. for 5 hours, and the resin composition for the internal
semiconductive layer is prepared.
(B) Preparation of the resin composition for the moisture
crosslinking polyethylene insulation layer. Monomer fluid comprised
of 90 parts by weight of ethylene and 10 parts by weight of
1-butene is fluidized from the bottom side of a fluidized bed
toward the upside and it is polymerized at 90 degrees C., 2.5 MPa
of pressure, and Gmf5 in a gas phase fluidized bed in the presence
of a polymerization catalyst impregnated with chromium trioxide,
tetraisopropyl titanate, and (NH.sub.4).sub.2 SiF.sub.6 in a porous
silica support having a surface area of 300 square meters per gram,
70 microns of mean diameter, and 100 microns of pore diameter. A
granular product having a surface area of 1000 square centimeters
per gram, a bulk density of 0.4 gram per cubic centimeter, and a
mean particle size of 0.8 millimeter is obtained. It is comprised
of ethylene/butene-1 copolymer having a density of 0.920 gram per
cubic centimeter and a melt mass flow rate of 0.8 gram per 10
minutes.
100 parts by weight of the aforementioned granular linear low
density ethylene/butene-1 copolymer is preheated at a temperature
of 60 degrees C., and 2 parts by weight of vinyltrimethoxysilane
and 0.1 part by weight of dicumyl peroxide are preheated at a
temperature of 50 degrees C. All are transferred into a ribbon
mixer. They are mixed for 30 minutes with heating at a temperature
of 60 degrees C. Then the mixture is allowed to stand for 2 hours
while maintaining the temperature at 60 degrees C., and a linear
low density ethylene-butene-1 copolymer impregnated with an
unsaturated alkoxysilane and organic peroxide is obtained.
Separately, 1 part by weight of dibutyltin dilaurate and 2 parts by
weight of
tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane
are mixed with 100 parts by weight of high pressure low density
polyethylene having a density of 0.920 gram per cubic centimeter
and a melt mass flow rate of 0.8 gram per 10 minutes. They are
kneaded at a temperature of 150 degrees C. for 10 minutes with a
Banbury.TM. mixer and polyethylene blended with silanol
condensation catalyst and antioxidant is obtained after
pelletizing.
95 percent by weight of the aforementioned linear low density
ethylene/alpha-olefin copolymer impregnated with the unsaturated
alkoxysilane and organic peroxide is added to 5 percent by weight
of the aforementioned polyethylene blended with the silanol
condensation catalyst and antioxidant. They are mixed, and the
resin composition for moisture cross-linking insulation layer is
prepared.
(C) The strippable semiconductive resin composition for external
semiconductive layer is prepared as follows:
(a) 100 parts by weight of ethylene/vinyl acetate copolymer
containing 28 percent by weight vinyl acetate and having a melt
mass flow rate of 20 grams per 10 minutes and a density of 0.938
gram per cubic centimeter;
(b) 70 parts by weight of linear ethylene/butene-1 copolymer having
a melt mass flow rate of 0.8 gram per 10 minutes and a density of
0.922 gram per cubic produced by a gas phase and low pressure
process;
(c) 20 parts by weight of polypropylene having a melt mass flow
rate of 0.9 gram per 10 minutes and a density of 0.900 gram per
cubic centimeter;
(d) 5 parts by weight of silicone gum stock containing 1 percent by
weight methylvinylsilicone having a viscosity of 300,000
centistokes at 23 degrees C.
(e) 30 parts by weight of Ketjen black;
(f) 0.3 part by weight of 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne;
and
(g) 0.3 part by weight of
tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane.
(D) Preparation of common triple layer extruding machine
Three extruders mounting screen packs of 150 mesh, 250 mesh and 120
mesh, respectively, at the die plates are combined to make an
extruding machine having common triple layer cross heads
sequentially positioned as the internal semiconductive layer
extruder, insulation layer extruder, and external semiconductive
layer extruder.
(E) Production of moisture crosslinked polyethylene insulation
power cable
The components of the resin composition for internal semiconductive
layer, moisture crosslinking polyethylene resin composition, and
strippable semiconductive resin composition for external
semiconductive layer prepared as above are supplied to the internal
semiconductive layer extruder, moisture crosslinking polyethylene
layer extruder and external semiconductive layer extruder of the
triple layer common extruding machine, respectively.
The components are kneaded by heating at 130 degrees C. at the
internal semiconductive layer extruder, 220 degrees C. at the
moisture crosslinking polyethylene layer extruder and 220 degrees
C. at the external semiconductive layer extruder, and they are
simultaneously extruded on a conductive body of hard drawn copper
strand to make a 1 millimeter thick internal semiconductive layer,
a 4 millimeter thick moisture crosslinkable polyethylene insulation
layer and a 1 millimeter external semi-conductive layer. This
procedure results in the formation of a cable.
Then the extruded cable is exposed to steam at 80 degrees C. for 24
hours to complete the moisture crosslinking reaction. After drying,
the cable is covered with a polyvinyl chloride compound to make a 3
millimeter thick jacket layer, and the moisture crosslinked
polyethylene insulation power cable is produced.
The performance evaluation results of the moisture crosslinked
polyethylene insulation power cable is shown hereinafter.
(1) Interface smoothness: The interface between the moisture
crosslinked polyethylene insulation layer and the external
semiconductive layer is smooth, and it is not recognized as peaking
over a 300 micron diameter.
(2) Heat deformation ratio of the external semiconductive layer:
The thickness decrease rate is 1 percent and the heat endurance is
sufficient.
(3) Peeling test of the external semiconductive layer: The peel
strength is 1.5 kilograms per 0.5 inch and the strippability is
sufficient.
(4) Tensile strength of the external semiconductive layer: The
tensile strength is 15.2 MPa, and it is not torn when the external
semiconductive layer is stripped.
(5) Elongation of the external semi-conductive layer: The
elongation is 434 percent.
(6) Gel fraction of the moisture crosslinked polyethylene
insulation layer: The gel fraction is 62 percent indicating it is
sufficiently moisture crosslinked and its heat endurance is
sufficient.
(7) Extrusion processability: Melt mass flow rate is 55 grams per
10 minutes and the extrusion processability is sufficient.
(8) Volume specific resistance: The volume specific resistance is
35 ohm-centimeters, and it is in an appropriate level.
Example 2
(A) Preparation of the resin composition for the internal
semiconductive layer: 0.5 part by weight of
tetrakis[methylene-3-(3,5-di-butyl-4-hydroxyphenyl)propionate]methane
and 80 parts by weight of acetylene black are blended with 100
parts by weight of a high pressure process ethylene/ethyl acrylate
copolymer containing 23 percent by weight ethyl acrylate, and
having a melt mass flow rate of 10 grams per 10 minutes and a
melting point of 98 degrees C. The three components are kneaded at
130 degrees C. for 10 minutes, and cylindrically pelletized to
pellets, each 3 millimeters in diameter and 3 millimeters in
height. Then, 0.5 part by weight of
2,5-dimethyl-2,5-di(t-butylperoxy)hexyne, an organic peroxide, is
added to the pellets; the organic peroxide is evenly impregnated
into in the pellets by slow mixing at 70 degrees C. for 5 hours,
and the resin composition for the internal semiconductive layer is
prepared.
(B) Preparation of the resin composition for the moisture
crosslinking polyethylene insulation layer.
0.1 part by weight of dicumyl peroxide and 2 parts by weight of
vinyltrimethoxysilane are added to 100 parts by weight of a high
pressure process low density polyethylene having a melt mass flow
rate of 2 grams per 10 minutes and a density of 0.922 gram per
cubic centimeter, and a silane modified polyethylene is produced by
extruding theses components from the extruder at 230 degrees C.
Separately, a catalyst masterbatch is made by mixing 1 part by
weight of dibutyltin dilaurate and 5 parts by weight of
tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane
with 100 parts by weight of high pressure low density polyethylene
having a density of 0.917 gram per cubic centimeter and a melt mass
flow rate of 3 grams per 10 minutes. The silane modified
polyethylene is then mixed with the master batch in a weight ratio
of 100 to 5. The resin composition for the moisture crosslinking
insulation layer is prepared.
(C) The strippable semiconductive resin composition for external
semiconductive layer is prepared as follows:
(a) 100 parts by weight of ethylene/ethyl acrylate copolymer
containing 32 percent by weight ethyl acrylate and having a melt
mass flow rate of 10 grams per 10 minutes and a density of 0.941
gram per cubic centimeter;
(b) 150 parts by weight of linear ethylene/hexene-1 copolymer
having a melt mass flow rate of 1.8 gram per 10 minutes and a
density of 0.935 gram per cubic produced by a solution process
using a single site metallocene catalyst;
(c) 40 parts by weight of propylene/ethylene copolymer containing 5
percent by weight ethylene and having a melt mass flow rate of 2.5
grams per 10 minutes and a density of 0.900 gram per cubic
centimeter;
(d) 45 parts by weight of silicone gum stock containing 0.7 percent
by weight methylvinylsilicone having a viscosity of 150,000
centistokes at 23 degrees C.
(e) 130 parts by weight of furnace black;
(f) 1.8 parts by weight of 2,5-dimethyl-2,5-di(tbutylperoxy)hexyne;
and
(g) 0.3 part by weight of
tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane.
(D) Preparation of common triple layer extruding machine and (E)
Production of moisture crosslinked polyethylene insulation power
cable of example 1 are repeated. The result is a jacketed cable
similar to that of example 1 except for the variations in
composition noted above.
The performance evaluation results of the moisture crosslinked
polyethylene insulation power cable are shown hereinafter.
(1) Interface smoothness: The interface between the moisture
crosslinked polyethylene insulation layer and the external
semiconductive layer is smooth, and it is not recognized as peaking
over a 300 micron diameter.
(2) Heat deformation ratio of the external semiconductive layer:
The thickness decrease rate is 1.4 percent and the heat endurance
is sufficient.
(3) Peeling test of the external semiconductive layer: The peel
strength is 1.6 kilograms per 0.5 inch and the strippability is
sufficient.
(4) Tensile strength of the external semiconductive layer: The
tensile strength is 12.8 MPa, and the layer is not torn when the
external semi-conductive layer is stripped.
(5) Elongation of the external semi-conductive layer: The
elongation is 381 percent.
(6) Gel fraction of the moisture crosslinked polyethylene
insulation layer: The gel fraction is 59 percent indicating it is
sufficiently moisture crosslinked and its heat endurance is
sufficient.
(7) Extrusion processability: Melt mass flow rate is 45 grams per
10 minutes and the extrusion processability is sufficient.
(8) Volume specific resistance: The volume specific resistance is
35 ohm-centimeters, and it is at an appropriate level.
Example 3
Example 1 is repeated except that the strippable semiconductive
resin composition for the external semiconductive layer is as
follows:
(a) 100 parts by weight of ethylene/butyl acrylate copolymer
containing 17 percent by weight butyl acrylate and having a melt
mass flow rate of 5 grams per 10 minutes and a density of 0.937
gram per cubic centimeter.
(b) 100 parts by weight of linear ethylene/hexene-1 copolymer
having a melt mass flow rate of 20 grams per 10 minutes and a
density of 0.900 gram per cubic centimeter produced in the gas
phase by a low pressure process.
(c) 7 parts by weight of polypropylene having a melt mass flow rate
of 1.2 grams per 10 minutes and a density of 0.910 gram per cubic
centimeter.
(d) 30 parts by weight of dimethylpolysiloxane oil containing 0.8
percent by weight methylvinylsilicone having a viscosity of 3,000
centistokes at 23 degrees C.
(e) 20 parts by weight of Ketjen black.
(f) 1.8 part by weight of
2,5-dimethyl-2,5-di(t-butylperoxy)hexyne.
(g) 0.3 part by weight of
tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane.
The results are as follows
(1) Interface smoothness: The interface between the moisture
crosslinked polyethylene insulation layer and the external
semiconductive layer is smooth, and it is not recognized as peaking
over 300 microns in diameter.
(2) Heat endurance of the external semiconductive layer: The
thickness decrease rate is 1.1 percent and the heat endurance is
sufficient.
(3) Peeling test of the external semi-conductive layer: The peel
strength is 1.9 kilograms per 0.5 inch and the strippability is
sufficient.
(4) Tensile strength of the external semiconductive layer: The
tensile strength is 10.6 MPa, and the layer is not torn.
(5) Elongation of the external semiconductive layer: The elongation
is 420 percent.
(6) Gel fraction of the moisture crosslinked polyethylene
insulation layer: The gel fraction is 59 percent. It is found to be
sufficiently moisture crosslinked and its heat endurance is
sufficient.
(7) Extrusion processability: The melt mass flow rate is 62 grams
per 10 minutes and the extrusion processability is sufficient.
(8) Volume specific resistance: The volume specific resistance is
53 ohm-centimeters and it is at an appropriate level.
Comparative Example 1
Example 1 is repeated except that the ethylene/vinyl acetate
copolymer is replaced with an ethylene/vinyl acetate copolymer
containing 8 percent by weight vinyl acetate. It is found that the
flexibility and elongation of external semiconductive layer has
deteriorated.
Comparative Example 2
Example 1 is repeated except that the ethylene/vinyl acetate
copolymer is replaced with an ethylene/vinyl acetate copolymer
containing 55 percent by weight vinyl acetate. It is found that the
tensile strength of the external semiconductive layer drops, and
the stripping of the external semiconductive layer becomes
difficult.
Comparative Example 3
Example 1 is repeated except that the ethylene/vinyl acetate
copolymer is replaced with an ethylene/vinyl acetate copolymer
having a melt mass flow rate of 0.8 gram per 10 minutes. It is
found that the extrusion processability, flexibility, and
elongation become insufficient.
Comparative Example 4
Example 1 is repeated except that the ethylene/vinyl acetate
copolymer is replaced with an ethylene/vinyl acetate copolymer
having a melt mass flow rate of 120 grams per 10 minutes. It is
found that the tensile strength and heat endurance of the external
semiconductive layer become insufficient.
Comparative Example 5
Example 1 is repeated except that the ethylene/butene-1 copolymer
is replaced with an ethylene/butene-1 copolymer having a melt mass
flow rate of 0.08 gram per 10 minutes. It is found that the
processability of the external semiconductive layer has
deteriorated.
Comparative Example 6
Example 1 is repeated except that the ethylene/butene-1 copolymer
is replaced with an ethylene/butene-1 copolymer having a melt mass
flow rate of 35 grams per 10 minutes. It is found that the tensile
strength of the external semiconductive layer has weakened.
Comparative Example 7
Example 1 is repeated except that the ethylene/butene-1 copolymer
is replaced with an ethylenelbutene-1 copolymer having a density of
0.850 gram per cubic centimeter. It is found that the heat
deformation ratio at and above 120 degrees C. of the external
semiconductive layer has deteriorated.
Comparative Example 8
Example 1 is repeated except that the ethylene/butene-1 copolymer
is replaced with an ethylene/butene-1 copolymer having a density of
0.948 gram per cubic centimeter. It is found that the flexibility
of the external semiconductive layer has deteriorated.
Comparative Example 9
Example 1 is repeated except that the amount of ethylene/butene-1
copolymer is changes to 50 parts by weight. It is found that the
heat deformation ratio at and above 120 degrees C. of the external
semiconductive layer has deteriorated.
Comparative Example 10
Example 1 is repeated except that the amount of ethylene/butene-1
copolymer is changes to 220 parts by weight. It is found that the
flexibility, elongation, and carbon black filling properties of the
external semiconductive layer have deteriorated.
Comparative Example 11
Example 1 is repeated except that the polypropylene is replaced
with a polypropylene having a melt mass flow rate of 0.3 gram per
10 minutes. It is found that the processability of the external
semiconductive layer has deteriorated.
Comparative Example 12
Example 1 is repeated except that the polypropylene is replaced
with a polypropylene having a melt mass flow rate of 33 grams per
10 minutes. It is found that the tensile strength of the external
semiconductive layer has weakened.
Comparative Example 13
Example 1 is repeated except that the polypropylene is replaced
with a polypropylene having a melt mass flow rate of 2 grams per 10
minutes and a density of 0.895 gram per cubic centimeter. It is
found that the heat deformation ratio at and above 120 degrees of
the external semiconductive layer has deteriorated.
Comparative Example 14
Example 1 is repeated except that the polypropylene is replaced
with a polypropylene having a melt mass flow rate of 5.4 grams per
10 minutes and a density of 0.925 gram per cubic centimeter. It is
found that the flexibility of the external semiconductive layer has
deteriorated.
Comparative Example 15
Example 1 is repeated except that the amount of polypropylene is
changed to 3 parts by weight. It is found that the heat deformation
ratio and strippability of the external semiconductive layer become
insufficient.
Comparative Example 16
Example 1 is repeated except that the amount of polypropylene is
changed to 55 parts by weight. It is found that the flexibility and
cold temperature resistance of the external semiconductive layer
have deteriorated.
Comparative Example 17
Example 1 is repeated except that the amount of silicone gum stock
is changed to 0.3 part by weight. It is found that the interface
smoothness and strippability become insufficient.
Comparative Example 18
Example 1 is repeated except that the amount of silicone gum stock
is changed to 55 parts by weight. It is found that the
processability and interface smoothness have deteriorated, and the
tensile strength becomes insufficient.
Comparative Example 19
Example 1 is repeated except that the amount of Ketjen black is
changed to 5 parts by weight. It is found that the volume specific
resistance of the external semiconductive layer is 200
ohm-centimeters.
Comparative Example 20
Example 1 is repeated except that the amount of Ketjen black is
changed to 430 parts by weight. It is found that the tensile
strength, processability, flexibility, and elongation of the
external semiconductive layer become insufficient.
Comparative Example 21
Example 1 is repeated except that the amount of organic peroxide is
changed to 2.3 parts by weight. It is found that many peaks are
produced on the surface of the semiconductive layer and a smooth
surface is not obtained.
* * * * *